In general, a side airbag is mounted inside a vehicle to secure protection for the passenger's chest and pelvis in a collision.
For the protection, the side airbag includes an inflator that generates high-pressure inflation gas by burning a gas generating agent in response to an inflation signal inputted in a collision and a cushion that is inflated toward the side of a passenger by the inflation gas supplied from the inflator.
The above cushion is formed by sewing the edges of two fabrics such that sealed spaces are formed inside the fabrics and the upper and lower portions of the cushion have the same volume when inflation is finished, such that the upper portion of the cushion contacts the passenger's chest and the lower portion contacts the passenger's pelvis.
However, the chest of a human body is composed of the ribs that are structurally weak relative to the pelvis, such that when a side airbag with a cushion having the same shock-absorbing performance is used, the damage to a passenger caused by a collision is relatively larger at the chest than the pelvis.
Therefore, proper measures should be variously devised for the side airbag in design to minimize damage to the passenger's chest.